Building or renovating a house involves dozens of technical, financial, and regulatory decisions. Since September 1, 2026, the rules of the game have changed for energy renovation aids, directly altering the way a project is conceived. Comparing expense items, anticipating administrative constraints, and choosing the right technical setup has become an exercise where each decision impacts the final budget and the duration of the construction.
Global renovation or isolated action: what the new MaPrimeRénov’ rules concretely change
| Criterion | Before September 2026 | Since September 2026 |
|---|---|---|
| Insulation only (walls, attics) | Eligible in action-by-action pathway | Removed from action-by-action pathway |
| Ventilation only (VMC) | Eligible in action-by-action pathway | Removed from action-by-action pathway |
| Solar thermal only | Eligible in action-by-action pathway | Removed from action-by-action pathway |
| Fossil heating in aided renovation | Tolerated under conditions | Prohibited (installation or maintenance) |
| Reference date for the applicable regime | Date of commitment to the work | Date of submission of the file |
This table summarizes the main changes published in the Official Journal on August 27, 2026. The refocusing on global renovation rather than isolated actions forces a rethink of the sequence of work from the design phase.
For a new construction project, the constraint is different: the RE 2020 already imposes strict energy performance thresholds. In renovation, it is the removal of the action-by-action pathway that reshuffles the cards. A homeowner who planned to insulate only the walls before addressing ventilation the following year now loses access to aid for the first item taken separately.
Resources like projet-habitat.fr help structure a project while considering these regulatory developments, particularly in coordinating the various technical lots with each other.
Construction and renovation budget: the areas where the gap widens
The temptation to compare only the cost per square meter between new construction and heavy renovation obscures disparities by item. Three budget lines concentrate most of the surprises.
The heating and hot water technical lot
The prohibition of fossil equipment in aided renovations since September 2026 mechanically increases the heating cost for houses equipped with an oil or gas boiler. Replacing it with a heat pump or a wood/biomass system represents a higher initial investment, even if operating costs decrease afterward.
In new construction, this item is integrated from the start into the RE 2020 calculation. Therefore, the cost gap between the two scenarios lies less in the equipment itself than in the related work: adapting the existing hydraulic network, reinforcing the electrical panel, ensuring compliance of the ventilation.
The land and soil study
In construction, the soil study (geotechnical study G2) determines the type of foundations. A clayey site subject to shrink-swell can significantly multiply the cost of foundations. In renovation, this study remains relevant as soon as an extension or elevation is considered, a point that many project owners discover too late.
The walls and insulation
Insulating existing walls from the inside reduces the living space. Insulating from the outside costs more but preserves interior space and addresses thermal bridges. The choice between interior and exterior insulation conditions the overall budget well beyond the insulation item alone, as it impacts finishes, joinery, and sometimes urban planning permits.
Submission calendar and administrative procedures: the timing trap
The date of submission of the MaPrimeRénov’ file now determines the applicable regime. A file submitted on August 31, 2026, fell under the old system. A file submitted on September 1 falls under the new one. This shift without a transitional period has caught many project holders off guard.
Securing the submission date before signing quotes becomes a structuring step. Concretely, this means that the administrative calendar takes precedence over the technical calendar: it is better to submit a complete file even if the work does not start for several months.
For new construction, the procedures differ but follow the same sequencing logic:
- The building permit must be obtained before any work begins, with a processing time that varies depending on the municipality and the complexity of the project (an architect is mandatory beyond a certain surface area threshold)
- The declaration of opening of the site must be submitted to the town hall so that the insurances (particularly damage insurance) are activated correctly
- The RE 2020 compliance certificate is required upon completion, which imposes checking the actual performance of the building (air tightness test, thermal measurements)
Project manager, architect, or self-management: deciding based on the complexity of the site
Hiring an architect is mandatory for any construction exceeding a certain floor area threshold. In renovation, this obligation also applies when the work modifies the structure or façade of a building subject to heritage regulations.
Beyond the legal obligation, the question is about the relationship between the cost of project management and the errors it avoids. An architect or project manager coordinates the lots, checks the compliance of quotes, and oversees execution. On a global renovation site involving insulation, ventilation, and replacement of the heating system, the coordination between these three items determines the final performance of the housing.
Self-managing a site remains possible for finishing work (painting, flooring, interior layout). As soon as the structural work or energy performance is at stake, the lack of technical coordination increases the risk of defects and non-compliance with regulatory requirements.
- Check that each craftsman has valid ten-year insurance for the relevant lot
- Compare at least three detailed quotes item by item, not just on the total amount
- Require a provisional schedule with intermediate reception milestones for each lot
The tightening of MaPrimeRénov’ around global renovation and the exclusion of fossil equipment change the game for any project launched after September 2026. The administrative calendar, long treated as a formality, becomes a significant financial lever. Documenting each step, from file submission to work completion, remains the best protection against unforeseen costs.
